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Title: The Discovery of λ Bootis Stars: The Southern Survey I

Abstract

The λ Boo stars are a class of chemically peculiar Population I A-type stars characterized by under-abundances of the refractory elements, but near-solar abundances of carbon, nitrogen, oxygen, and sulfur. There is some evidence that λ Boo stars have higher frequencies of “bright” debris disks than normal A-type stars. The discovery of four exoplanets orbiting HR 8799, a λ Boo star with a resolved debris disk, suggests that the λ Boo phenomenon may be related to the presence of a dynamic debris disk, perhaps perturbed by migrating planets. However, only 64 λ Boo stars are known, and those stars were discovered with different techniques, making it problematic to use that sample for statistical purposes, including determining the frequency of debris disks. The purpose of this paper is to derive a new sample of λ Boo stars using a technique that does not lead to biases with respect to the presence of infrared excesses. Through spectroscopic observations in the southern hemisphere, we have discovered 33 λ Boo stars and have confirmed 12 others. As a step toward determining the proportion of λ Boo stars with infrared excesses, we have used WISE data to examine the infrared properties of this sample outmore » to 22 μ m. On this basis, we cannot conclude that λ Boo stars have a greater tendency than normal A-type stars to show infrared excesses. However, observing this sample at longer wavelengths may change that conclusion, as many λ Boo debris disks are cool and do not radiate strongly at 22 μ m.« less

Authors:
; ;  [1];  [2];  [3];  [4];  [5];  [6]
  1. Department of Physics and Astronomy, Appalachian State University, Boone, NC 26808 (United States)
  2. Department of Statistics, University of the Western Cape, Private Bag X17, Bellville, 7535 Cape Town (South Africa)
  3. Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006 (Australia)
  4. Vatican Observatory Research Group, Steward Observatory, Tucson, AZ, 85721-0065 (United States)
  5. California State University, Fullerton, Fullerton, CA (United States)
  6. National Science Foundation, Arlington, VA (United States)
Publication Date:
OSTI Identifier:
22663442
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 154; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON; ELEMENT ABUNDANCE; EMISSION; NITROGEN; OXYGEN; REFRACTORIES; SOUTHERN HEMISPHERE; STAR EVOLUTION; STARS; SULFUR; WAVELENGTHS

Citation Formats

Gray, R. O., Riggs, Q. S., Newsome, I. M., Koen, C., Murphy, S. J., Corbally, C. J., Cheng, K.-P., and Neff, J. E. The Discovery of λ Bootis Stars: The Southern Survey I. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA6D5E.
Gray, R. O., Riggs, Q. S., Newsome, I. M., Koen, C., Murphy, S. J., Corbally, C. J., Cheng, K.-P., & Neff, J. E. The Discovery of λ Bootis Stars: The Southern Survey I. United States. doi:10.3847/1538-3881/AA6D5E.
Gray, R. O., Riggs, Q. S., Newsome, I. M., Koen, C., Murphy, S. J., Corbally, C. J., Cheng, K.-P., and Neff, J. E. Sat . "The Discovery of λ Bootis Stars: The Southern Survey I". United States. doi:10.3847/1538-3881/AA6D5E.
@article{osti_22663442,
title = {The Discovery of λ Bootis Stars: The Southern Survey I},
author = {Gray, R. O. and Riggs, Q. S. and Newsome, I. M. and Koen, C. and Murphy, S. J. and Corbally, C. J. and Cheng, K.-P. and Neff, J. E.},
abstractNote = {The λ Boo stars are a class of chemically peculiar Population I A-type stars characterized by under-abundances of the refractory elements, but near-solar abundances of carbon, nitrogen, oxygen, and sulfur. There is some evidence that λ Boo stars have higher frequencies of “bright” debris disks than normal A-type stars. The discovery of four exoplanets orbiting HR 8799, a λ Boo star with a resolved debris disk, suggests that the λ Boo phenomenon may be related to the presence of a dynamic debris disk, perhaps perturbed by migrating planets. However, only 64 λ Boo stars are known, and those stars were discovered with different techniques, making it problematic to use that sample for statistical purposes, including determining the frequency of debris disks. The purpose of this paper is to derive a new sample of λ Boo stars using a technique that does not lead to biases with respect to the presence of infrared excesses. Through spectroscopic observations in the southern hemisphere, we have discovered 33 λ Boo stars and have confirmed 12 others. As a step toward determining the proportion of λ Boo stars with infrared excesses, we have used WISE data to examine the infrared properties of this sample out to 22 μ m. On this basis, we cannot conclude that λ Boo stars have a greater tendency than normal A-type stars to show infrared excesses. However, observing this sample at longer wavelengths may change that conclusion, as many λ Boo debris disks are cool and do not radiate strongly at 22 μ m.},
doi = {10.3847/1538-3881/AA6D5E},
journal = {Astronomical Journal (Online)},
number = 1,
volume = 154,
place = {United States},
year = {Sat Jul 01 00:00:00 EDT 2017},
month = {Sat Jul 01 00:00:00 EDT 2017}
}
  • This paper presents 442 new proper motion stellar systems in the southern sky between declinations -90{sup 0} and -47{sup 0} with 0.''40 yr{sup -1} > {mu} {>=} 0.''18 yr{sup -1}. These systems constitute a 25.3% increase in new systems for the same region of the sky covered by previous SuperCOSMOS RECONS (SCR) searches that used Schmidt plates as the primary source of discovery. Among the new systems are 25 multiples, plus an additional 7 new common proper motion (CPM) companions to previously known primaries. All stars have been discovered using the third U.S. Naval Observatory (USNO) CCD Astrograph Catalog (UCAC3).more » A comparison of the UCAC3 proper motions to those from the Hipparcos, Tycho-2, Southern Proper Motion (SPM4), and SuperCOSMOS efforts is presented and shows that UCAC3 provides similar values and precision to the first three surveys. The comparison between UCAC3 and SuperCOSMOS indicates that proper motions in R.A. are systematically shifted in the SuperCOSMOS data but are consistent in decl. data, while overall showing a significantly higher scatter. Distance estimates are derived for stars having SuperCOSMOS Sky Survey B{sub J} , R{sub 59F}, and I{sub IVN} plate magnitudes and Two-Micron All Sky Survey infrared photometry. We find 15 systems estimated to be within 25 pc, including UPM 1710-5300 our closest new discovery estimated at 13.5 pc. Such new discoveries suggest that more nearby stars are yet to be found in these slower proper motion regimes, indicating that more work is needed to develop a complete map of the solar neighborhood.« less
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  • A search for magnetic fields in southern Ap stars has been made using a Balmer-line magnetograph. Observations of nine stars were obtained, and definite or probable evidence for the presence of fields ranging from a few hundred gauss to almost four kilogauss was found in HD 54118, HD 94660, HD 133880, and $alpha$ Cir. (auth)
  • Here we present 1584 new southern proper motion systems with {mu} {>=} 0.''18 yr{sup -1} and 16.5 > R{sub 59F} {>=} 18.0. This search complements the six previous SuperCOSMOS-RECONS (SCR) proper motion searches of the southern sky for stars within the same proper motion range, but with R{sub 59F} {<=} 16.5. As in previous papers, we present distance estimates for these systems and find that three systems are estimated to be within 25 pc, including one, SCR 1546-5534, possibly within the RECONS 10 pc horizon at 6.7 pc, making it the second nearest discovery of the searches. We find 97more » white dwarf candidates with distance estimates between 10 and 120 pc, as well as 557 cool subdwarf candidates. The subdwarfs found in this paper make up nearly half of the subdwarf systems reported from our SCR searches and are significantly redder than those discovered thus far. The SCR searches have now found 155 red dwarfs estimated to be within 25 pc, including 10 within 10 pc. In addition, 143 white dwarf candidates and 1155 cool subdwarf candidates have been discovered. The 1584 systems reported here augment the sample of 4724 systems previously discovered in our SCR searches and imply that additional systems fainter than R{sub 59F} = 18.0 are yet to be discovered.« less